This blog discusses current weather, weather prediction, climate issues, and other topics

Sunday, July 17, 2011

Did Sea-Tac's Third Runway Change Our Climate?

Last week the Seattle Times had a front page story about the Northwest becoming warmer and wetter based on recently updated climate statistics at Seattle-Tacoma Airport. But can we use one observing site to reliably determine region climate trends? In my previous blog I noted that this is a real problem: one site is not necessarily representative of a region and besides it might have observing issues. And Sea Tac has such issues in spades: changes in the local environment, changes in sensors, and changing positions of the sensors.

But there is a related issue: although I believe that the threat of anthropogenic global warming forced mainly by CO2 and other greenhouse gases is extraordinarily serious and --quite frankly-- inevitable, I also worry about the integrity of our surface observations. I don't believe my field has given sufficient attention to the impact of development around our weather stations, or of poor placement of our thermometers near concrete, buildings, or other generators of heat.

So let us consider Seattle-Tacoma Airport, clearly the most reported station in western Washington and one frequently cited as a harbinger of climate change (such as in the Seattle Times).

Between 2004 and 2008 there was a huge change at the airport, one of the largest construction/earth moving projects in the region in years--the building of a third runway. In this blog I will ask the question: did the construction of the third runway have an impact on summer temperatures reported from the airport? My conclusion and that of my colleague Mark Albright is: it sure looks like it.

But first a few pictures. Here is a picture of Sea-Tac before the third runway was installed. I have also indicated the position of the National Weather Service/FAA temperature sensors (their ASOS system) by a blue circle (just to the west of the second runway).

Although it is hard to see, just to the west of the weather sensors the ground sloped down a hill (Sea-Tac is on a high spot), a hill that had lots of vegetation. During the summer, particularly during the afternoons, the winds are from the northwest, and thus the air reaching that sensor was from above that vegetated hill. Vegetation keeps daily temperatures down (mainly from evaporation of water--transpiration) and the higher you are above the surface in summer, the cooler the air.

In 2004 construction began on the third runway--a huge task. Massive amounts of fill were brought in to the west side of the airport--just where that vegetated hill was located. And a huge new concrete runway, with all kinds of taxiways and ancillary roads, were built. A massive change of the surface west of the sensor.

Here are two recent pictures of the current runway situation (with the blue circle showing the sensor position). Quite a change.

Here is a close of view of the sensors based from an image available on Google maps:

Now I did quite a lot of research to determine whether there were any temperature sensor changes recently (position, type, etc) at the airport and have reached lots of assistance from the folks at Sea Tac Airport and the National Weather Service. Based on their help, and the documentation available from the National Climatic Data Center, I think we can say, quite authoritatively, that the temperature sensor has has not been moved since 2002 ( it had been shifted a bit then in consideration of the third-runway construction, and there had been major moves/sensor changes in previous years).

OK, now lets answer the question. Did the runway change the summer climate at the airport? My colleague, Mark Albright, calculated the difference in summer temperatures (June, July, August) between Sea-Tac and an average of four nearby official reporting locations (Olympia, McMillan Reservoir near Tacoma, Kent, and Buckley).

Negative means that the neighbors are warmer than Sea-Tac, which you would expect since they are farther inland and generally south of Sea-Tac (which has some cooling influence from the Sound). You will see that Sea-Tac was generally cooler than those surrounding station (by roughly 1.5F) early in the period. And the slight shift in 2002 had little impact. But after construction began in 2004 (particularly in 2005 to 2006 when the heavy earth moving occurred) things changed: Sea-Tac temperatures warmed up by roughly 2F so it was the same or warmer than the surrounding, more inland, stations. I strongly suspect we are seeing the influence of the third runway.

The impact of development at the runway is also suggested by looking at recent temperatures at truly neighboring observing locations (not all official). For example, here is a plot of temperatures during the afternoon of July 15th in the Sea-Tac neighborhood at 4 PM (click to enlarge). Sea-Tac is the warmest of the bunch at 74F!

Bottom line: It really looks that the third runway has significantly warmed summer temperatures at the airport. Thus, one must be really careful in assuming that any warming there is the result of some kind of greenhouse gas influence.

Now this is not the only site with problems, a very significant percentage of our observing sites have moved, had sensor changes, are in areas in which urbanization have occurred, or other issues. This makes it very difficult to use surface data to secure reliable information on regional temperature trends. It is possible, but one has to spend considerable time to remove the bad stations or make reasonable adjustments. Much more work needs to be done in this area.

40 comments:

Another great post! At the risk of sparking endless debate about climate change (that's not what prompts this question), could this same sort of thing affect data collected over the past 100 years? And what about the method of collecting such data? The thermometers, the mercury in them, and so on? Could small changes over the years affect the data? Thanks for a great blog!

Without a doubt the third runway has increased air traffic. And with it noise. We really notice it locally on Vashon Island. There is also an increase of pollution from this increased activity. How does that affect local weather and health?

I have often wondered the same thoughts; it appears that when the original recording station, which was, I believe at the Seattle Times in downtown Seattle, moved to SeaTac in the ‘60s, we also had a significant change in our weather. (As recorded.)

Another factor that might play a part is the industrialization of the Kent Valley. Building up the Bow Lake airfield to become SeaTac was the result of weather conditions; no fog compared to Boeing Field. After the late ‘60s when paving the Kent Valley started, significant fog started to affect SeaTac. As I understand it, warmer air heated from industry in the Kent Valley rolling up the hill to meet cooler moist air from the sound equals fog and lots of it.

Is there any consistently operated reporting station in the region that has not been moved or impacted over the last century?

You mentioned this possibility quite a while back, and am glad you have the data to back up the theory now.

I've always thought any "airport" data in any metro area ends up being skewed by the "heat" island effect. Too much asphalt and concrete, not enough vegetation nearby the ASOS to offset the radiated heat at night... thus altering minimums to read much higher, which buggers up the daily avg temps.

I cannot escape the conclusion that this weather station has been, and certainly now is, improperly sited. It measures warmer temperatures than it should due to the local heating effect of the airport.

Yet data from such stations are the basis for long term climate studies, and in Cliff's case, short term weather forecasts. Is there any wonder why people remain skeptical about both climate and weather forecasting? The Seatac station data is of poor quality going into the models. Therefore so are the model outputs poor, and so are the resulting forecasts.

"could this same sort of thing affect data collected over the past 100 years?"

The effect of urbanization - urban "heat islands" - is very real.

Fortunately we have other records, such as oxygen-18/16 ratios measured from ice cores, that also provide a proxy temperature record from the past (both recent and long-term). Those also, pretty consistently, show a significant temperature increase since the onset of industrialization... and a more marked increase over the past 20-30 years.

Cliff, given all this data uncertainty, do you advocate a "wait and see" approach to taking action on global warming? It seems like your posts on the topic support the position of those who say we should wait for more data before expending effort on mitigating carbon emissions.

Good reporting and science Cliff. This combined with your last post shows why the average world citizen is unwilling to stand by as out governments and representatives chase dubious "problems" with billions of tax dollars.

Now I think you happen to be the most accurate and knowledgeable meteorologist I have ever read. But, just a few weeks ago you said that our summer weather pattern was here to stay. And now we have a low parked off the coast. This stuff is chaotic and complex. No serious predictions can be made for any sort of term that I have ever seen. Similarly, Climatologists have forecast massive warming, only to have it stop since 1998.

Could the sun and the Pacific ocean's heat storage have more to do with our climate than humans? Serious scientists believe there is far more at work here than SUVs and factories.

Thanks for being a serious scientist and not a political activist like James Hansen.

Except that the Global Climate Change denier argument of flawed surface data (heat island effect) has been debunked. Statistically those instruments sited close to buildings, etc. are offset by those that aren't and the data they show shows the same results: It's getting warmer.

Sounds as if the more immediate solution to this basic integrity problem, is - or would be, to work first to isolate just which stations both are and also look to remain, more viable, and then for whatever agencies / organizations to offer some parameters' output relying on them more alone. — perhaps more "experimentally", as it were, more initially.

Cliff,Perhaps we'd all be well served by a combined temperature reading/record from our local area that would take the data from ,say, 10 sites that you consider to be representative of the various microclimates of Seattle. This combined reading would be much less influenced by the heat island effect and microclimate variations, and could thus serve as way to get rid of the data clutter and show trends more accurately.'2 cents' Isaac Great post by the way.

Global warming is a GLOBAL issue, and the issues with the Seatac data have been DEMONSTRATED not to be a general issue (see ImTurningIt, 8:20). This in no way contradicts Cliff's inference of an artificial step in reported in Seatac temperatures.

Cliff's analysis remains of interest on many levels - regional trends, instrumentation, scientific misinterpretation. At least I though it was, and I am already intimately familiar with good and bad scientific data. Why are you reading this?

@Alex (11:41)

You can't be serious. Do you really think the dominant feature of global warming is the temperature in the northwest for a few years?

Now it's not only the third runway, but it's those @#$% asteroids!:Asteroids are making Earth’s weather unpredictableNo, ceres-iously! asteroids cause more chaotic orbits so (long term, one presumes) climate is harder to predict. so the next time your Bite-of-[insert_city] is rained out raise your fist and shout: "damn you '433-Eros' may '2002-AT4' collide into you and destroy your albedo!" i know i will.

Something is bothering you about this discussion, as you call for more sciency comments, so I'll guess that your question was not answered explicitly enough.

The SEATAC sensor is providing correct data after all?

No, Cliff makes an excellent case that the temperature step is an artifact. And the case for global warming is not built on the single data point from Seatac, nor on an absence of such artifacts. In fact the influence of such known artifacts has been comprehensively investigated and shown to be minimal.

Hmmm, a new avatar makes obtusely provocative posts, disrupting than promoting understanding of climate science. One might guess which POV debates this way.

This is a great post, and I am happy to see a 'peer' in the climate science community challenge the status-quo, which has by and large used extremely poor scientific test and analysis. I do not believe that anthropogenic climate change is a dominant factor in our weather, but I am willing to be convinced if the science presented as proof were objective, disciplined and thorough, and not the goal-oriented, government-funded whore that it has it has proven to be.

Nason wrote:"This is a great post, and I am happy to see a 'peer' in the climate science community challenge the status-quo, which has by and large used extremely poor scientific test and analysis. "

You are misreading, I think. Cliff is concerned because siting issues present problems for studying regional climate trends. The validity of global warming and the fact that it is primarily caused by humans is not in question here.

See Menne, et al 2010 for a discussion of the impact of station siting and quality on measurements of global average temperature anomalies. The summary is: "poorly" sited stations, on average, show the same warming trend and similar annual anomalies as the "best" sited stations. In fact, the two reconstructions based upon the "best" and "poorest" stations are virtually indistinguishable.

Further, see http://tamino.wordpress.com/2011/07/13/bob-carter-does-his-business/ for a discussion of the surface station record quality wrt the global average temperature anomaly. Summary: the three surface records tracks well with the two satellite records.

Granted, this is the annual average anomaly, and the main point here is that if we want to make headway on understanding regional trends and effects, we need to improve our management of our surface stations.

'Analysis of the impacts of station exposure on the U.S. Historical Climatology Network temperatures and temperature trends'

Journal of Geophysical Research

"....Comparison of observed temperatures with NARR shows that the most poorly-sited stations are warmer compared to NARR than are other stations, and a major portion of this bias is associated with the siting classification rather than the geographical distribution of stations.

According to the best-sited stations, the diurnal temperature range in the lower 48 states has no century-scale trend."

Your point seems quite valid, but a good test would be to compare low and high temps to the surrounding stations. One would expect the low temps to show an even higher deviance due to nighttime radiance.

The role of Urban Heat Islands is addressed in climate change research - in part by doing just what Cliff has done here and comparing urban vs rural stations.

From the IPCC Third Assessment Report, section 2.2.2.1 "Land-surface air temperature"

"While there is little difference in the long-term (1880 to 1998) rural (0.70°C/century) and full set of station temperature trends (actually less at 0.65°C/century), more recent data (1951 to 1989), as cited in Peterson et al. (1999), do suggest a slight divergence in the rural (0.80°C/century) and full set of station trends (0.92°C/century). However, neither pair of differences is statistically significant. In addition, while not reported in Peterson et al., the 1951 to 1989 trend for urban stations alone was 0.10°C/decade. We conclude that estimates of long-term (1880 to 1998) global land-surface air temperature variations and trends are relatively little affected by whether the station distribution typically used by the four global analyses is used, or whether a special effort is made to concentrate on rural stations using elaborate criteria to identify them."

and later

"Note that changes in borehole temperatures (Section 2.3.2), the recession of the glaciers (Section 2.2.5.4), and changes in marine temperature (Section 2.2.2.2), which are not subject to urbanisation, agree well with the instrumental estimates of surface warming over the last century."

Though not directly pertinent to this particular blogpost, I just won't resist putting the following excerpt from today (7/19/11)'s 3:00 p.m. Seattle WFO NWS weather discussion while it was still easily accessible:

"Looking farther ahead...the longwave pattern with this persistent upper trough affecting western Washington may be getting ready to change. The GFS 5-wave chart shows this change toward the end of the month when the long wave trough position shifts from 135w to around 165w and a ridge is shown over the pacnw. That is beyond the forecast period for this forecast but the CPC forecast shows the outlook for temperatures below normal in the 6-10 day outlook warming to normal in the 8-14 day outlook."

I noted this shift in the 8-14 from the 6-10 day outlook earlier today, but I think it really says something when a NWS forecaster spends a paragraph to discuss a possible situation beyond the forecast period. Whether it ends up happening or not -- and the forecasters have been fooled more than once this summer on this type of thing -- it really would seem to show just how antsy people in the NW are getting for some NORMAL NW summer weather.

I would think the Sea-tac temp reading would be higher even from the sensor being between two runways, because of the exhaust. In the same way, busy main streets are usually significantly hotter than their arterial side streets one block away (regardless of foliage).

This is incredible posting and commentary, even though my area merely gets the leftovers (sans rain) of your weather, when plagued with a NW flow aloft.

Our own airport temps changed noticeably 10+ years ago, hardly ever getting record highs or lows since. It is forever at the edge of the urban area, but I don't recall the instruments moved enough or anything built like walls, another runway, etc.

Global warming / change - I take a moderate approach...some AGW, some natural cycles. I learned in the early 1980s as a high school student visiting Mesa Verde in SW Colorado, how the Anasazi were growing cotton. That would require it to be more moist, at least 7F warmer over the year than today, and a growing season of 200+ days.